Thermal response test (TRT) is a common procedure for characterization of ground and borehole thermal properties needed for the design of a shallow geothermal heat pump system. In order to investigate and to develop more accurate and robust procedures for TRT control, modelling, and evaluation in semi-permeable soils with large water content, a pilot borehole heat exchanger was built in the main campus of the Universitat Politècnica de València. The present work shows the results of the experiments performed at the site, analysing the improvements that have been introduced both in the control of the heat injected during TRTs and in the methods to infer the ground thermal parameter. Three models are compared: two based on the infinite-line source theory and one based on the finite-line source scheme. The models were tested under two possible configurations of the equipment, i.e., with and without strict control of injected heat. Our results show the importance of heat injection control for a robust parameter assessment and the existence of additional heat transfer processes that the used models cannot completely characterize and that are related to the presence of significant groundwater flow at the site. In addition, our experience with the current installation and the knowledge about its strengths and weaknesses have allowed us to design a new and more complete test-site to help in the analysis and validation of new ground heat exchanger geometries.

In ground-source heat-pump systems, the heat exchange rate is influenced by various design and operational parameters that condition the thermal performance of the heat pump and the running costs during exploitation. One less-studied area is the relationship between the pumping costs in a given system and the heat exchange rate. This work analyzes the investment and operating costs of representative borehole heat-exchanger configurations with varying circulating flow rate by means of a combination of analytical formulas and case study simulations to allow a precise quantification of the capital and operational costs in typical scenario. As a conclusion, an optimal flow rate minimizing either of both costs can be determined. Furthermore, it is concluded that in terms of operating costs, there is an operational pumping rate above which performance of geothermal systems is energetically strongly penalized.

The temporal evolution of the electrical signal generated by Pinus halepensis was measured in a sample of 15 trees. Weekly experiments were carried out during a long-term campaign lasting over a year, while trials with a high frequency of measurements were also performed during several days. In the latter case, day-night oscillations of the electrical magnitudes were observed. Additionally, punctual meteorological events such as rainfall and electrical storms affect the electrical signal as well. The measured electrical intensity grows exponentially with the voltage. In fact, no electrical intensity that exceeds the threshold of 0.01 μA is gathered when voltage values are lower than 0.6 V. In general, higher electrical signals were gathered during the rainy seasons with moderate temperatures; while very low signals, including few measures of zero intensity, were obtained during the most stressful periods over the year, mainly by mid-summer. There is a strong correlation between the rainfall and the electrical signal. The rain-intensity correlation, together with sustained intensity values during the reproductive period in spring, suggests that this electrical magnitude could be an indicator of the physiological state of the tree and thus used for in situ and minimally invasive forest monitoring.